1. Field of the Invention
This invention relates generally to apparatus for perforating moving webs of paper, film and like materials by intermittent or pulsed electric discharge and more particularly to apparatus for perforating cigarette paper in which the web of paper is drawn through the gap between electrically charged electrode means and ground electrode means whereby the web is perforated by intermittent arcing between electrodes as it passes between them.
2. Description of the Prior Art
Numerous devices have been developed for making perforations in paper and related web materials by pulsed electrical discharge. Typically, such devices utilize various types of pin or needle arrangements for the discharge electrodes in combination with a stationary or rotating member as the ground electrode, as shown in U.S. Pat. Nos. 3,098,143; 3,348,022; 3,385,951; 3,475,591; 3,760,153; 3,783,237; and 3,862,396. All of these devices suffer from the drawback that the discharge electrode pins tend to degrade rapidly by thermal erosion from the high heat generated during arcing between the pins and the ground electrode. Such degradation changes the gap between the electrodes and corrodes and insulates the point of the pin electrodes causing the pins to misfire resulting in nonuniform perforation of the web material.
Other types of electrodes have been employed such as spaced pairs of oppositely placed rotating wheels or discs between which the web material is passed, as disclosed in U.S. Pat. Nos. 2,372,508 and 3,167,641. While these devices have the advantage of periodically presenting a different surface for spark discharge, thereby reducing thermal erosion, they have the disadvantage of producing perforations in the sheet material of uneven size because the arcing point between electrodes cannot be precisely localized.
A method and apparatus that overcomes the disadvantages of the above prior art devices is disclosed in the application of Richard Hugo Martin, Ser. No. 654,201, filed Feb. 2, 1976, assigned to the same assignee as the assignee of the present application. However, one problem that has been encountered with the apparatus of said copending application is collection and removal of particulate matter produced during the perforating operation when the web to be perforated is paper, such as cigarette paper. The residue from the holes produced in the web builds up near the ground electrode and other areas under the web, requiring periodic shutdown of the apparatus for cleanup. Such residue is primarily calcium carbonate filler from the paper and the configuration of the grounding plate has not proved satisfactory for long-term operation of the electrostatic perforater because the particles build up on the plate causing the paper web to break, thereby reducing productivity.